This invention relates to a technique of managing performance of a storage system including virtualized storage extents, and more particularly, to a technique for equalizing loads on hardware resources.
A storage area network (SAN) is known as a technique of connecting one or more external storage devices and one or more computers to each other. The storage area network is in particular effective in a case where a plurality of computers share one large-scale storage device. In a storage system including the storage area network, it is possible to add or delete a storage device or a computer with ease, which means that the storage system excels in extensibility.
In general, as an external storage device connected to the SAN, a disk array device is often used. The disk array device is a device equipped with many magnetic storage devices represented by hard disk drives.
The disk array device uses a redundant array of independent disks (RAID) technique to manage several magnetic storage devices as one RAID group. The RAID group forms one or more logical storage extents. The computers connected to the SAN carry out processing for inputting/outputting data into/from the storage extents. When data is recorded in the storage extents, the disk array device records redundant data in the magnetic storage devices configuring the RAID group. By recording the redundant data in this manner, even when one of the magnetic storage devices has failed, it becomes possible to restore data.
To the SAN, it is possible to connect different kinds of storage subsystems. Therefore, it is required for an operation manager to exercise management while giving consideration to device characteristics, which increases a burden on him/her.
A virtual storage technique provides a host computer with a storage capacity equipped for a separately existing storage subsystem by virtualizing the storage capacity so that it is possible to deal with the storage capacity as a resource stored in a virtualized storage subsystem. Therefore, it becomes possible to collectively manage resources on different kinds of storage subsystems having different characteristics, which makes it possible to alleviate a management burden (refer to JP 2005-011277 A).
Further, in conventional SAN operation, when a storage volume is mounted to a file system operated by a host computer, it is required to statically allocate a corresponding physical disk capacity in advance. In addition, a vast number of steps including system halt, are required for capacity addition and volume creation and deletion.
A thin provisioning technique provides a host computer with a storage volume in virtual units instead of allocating a physical disk capacity in advance. In addition, when writing from the host has occurred, an extent is dynamically allocated from a storage resource pool. Therefore, it is only necessary that the storage resource pool defined in advance is configured using a capacity that is small as compared with a virtual volume, which improves capacity use efficiency. Still in addition, in pool capacity addition, no influence is exerted on the host computer, so operation is simplified and it becomes possible to alleviate management burden (refer to JP 2003-015915 A).
In this specification, a storage extent provided to a host computer with the virtual storage technique is referred to as the “external storage extent” and a storage extent provided to the host computer with the thin provisioning technique is referred to as the “virtual storage extent”, thereby distinguishing these storage extents from each other.